20-Spring Container

Question 1

Stereotype annotations

Answer 1

Component
Repository
Service
Controller
RestController
Configuration

Question 2

Meta-annotation

Answer 2

Annotation can be used to create new annotations e.g. @Service, @MockBean. Example:
@Service
public @interface MyService {}

Question 3

Bean initialization process

Answer 3

0. All instances of BeanPostProcessor have a chance to process before and after initialization
1. Bean created, properties and dependencies are set
2. @PostConstruct
3. afterPropertiesSet if a bean implements InitializingBean interface
4. init-method in
5. ## Ready to useNote: If the same init method has already been invoked, it will not be invoked again

Question 4

Bean deconstruction process

Answer 4

1. @PreDestroy
2. destroy (not dispose) method in DisposeableBean bean
3. ## destroy-method inNote: If the same destruction method has already been invoked, it will not be invoked again

Question 5

What are the use cases of spring.factories file?

Answer 5

1. Register application event listeners

2. Locate auto-configuration candidates

Question 6

What is the name of objects created by the Spring IoC container?

Answer 6

Beans

Question 7

Which of the following are valid ways of defining Spring bean metadata?

Answer 7

1. Java annotation
2. Java code
3. XML fields

Question 8

Why can I say “lifecycle management in Spring is consistent”?

Answer 8

regardless of the type of application - the way Spring behaves in a unit test is identical to how it will behave in production

Question 9

Why can I say “lifecycle management in Spring is lightweight”?

Answer 9

It does not require deploying applications to a servlet container or other special environment

Question 10

How to modify bean definitions?

Answer 10

1. Implement BeanFactoryPostProcessor
2. Override BeanFactoryPostProcessor.postProcessBeanFactory(…)
3. Create a static bean method so that it can be detected before other beans

Question 11

What does PropertySourcesPlaceholderConfigurer do?

Answer 11

A BFPP that evaluates @Value(“expression”) and

Question 12

List out 3 BFPP

Answer 12

1. PropertySourcesPlaceholderConfigurer
2. DeprecatedBeanWarner
3. CustomScopeConfigurer

Question 13

What bean enables @PostConstruct, how is it implemented?

Answer 13

CommonAnnotationBeanPostProcessor extends BeanPostProcessor

Override postProcessBeforeInitialization

Question 14

When does BeanPostProcessor.postProcessBeforeInitialization get called?

Answer 14

bean creation –> DI –> postProcessBeforeInitialization –> initializers called (e.g. InitializingBean’s afterPropertiesSet or a custom init-method)

Question 15

When does BeanPostProcessor.postProcessAfterInitialization get called?

Answer 15

bean creation –> DI –> postProcessBeforeInitialization –> initializers called (e.g. InitializingBean’s afterPropertiesSet or a custom init-method) –> postProcessAfterInitialization

Question 16

Input, output of BeanPostProcessor.postProcessBeforeInitialization

Answer 16

Object postProcessBeforeInitialization(Object originalBean, String beanName);
return post processed bean

Question 17

About JDK proxy

Answer 17

1. Also called dynamic proxies
2. Built-in in JDK
3. Requirements: Java interfaces
4. All interfaces proxied

Question 18

About CGLib proxy

Answer 18

1. Not build-in in JDK
2. Included in Spring jars
3. Used when interface is not available
4. Cannot be applied to final classes or methods

Question 19

How to force dependency order?

Answer 19

Using @DependsOn(value[])
Apply to component class and bean method

Question 20

What are type and beanName created in this case?
@Bean
TransferService tfService() {
    return new BankTransferServiceImpl();
}

Answer 20

type: TransferService (not BankTransferServiceImpl)
name: tfService

Question 21

Can CGLib prox private methods?

Answer 21

No, because it creates subclass of the target class so there’s no way to intercept private